Water transfer systems (WTS) have been developed to pass sea water or other fluid to be studied through multiple user replaceable sample collectors in a time series sequence. By way of example filters are used for sampling, collecting and studying suspended particles and various collector columns are used for sampling, collecting and testing selected molecules. The water transfer system includes a pump which draws the sea water or other fluid to be studied successively through the multiple collector sites. A multiport valve opens and closes the channels to the respective sampling sites. A programmable controller relays instructions programmed by a user for controlling the pump and multiport valve.
The WTS can be programmed by the user for collecting suspended particles or concentrating specified molecules in filters and column collectors in a desired time series sequence. For example, the user can specify the time, date, and interval duration for sample collection at each successive sampling site. The user can also specify the pumping rate, flow rate of water, and total quantity of water pumped through each successive sampling site.
Alternatively the WTS programmable controller can be preprogrammed with a back pressure threshold for example for use with multiple filters or collectors. As particles build up in the filter, the controller senses slow down in the speed of the drive motor that drives the pump which is in turn responsive to back pressure. The controller can be programmed to turn off the pump at the selected back pressure threshold. The next sampling occurs at a new filter location sampling site at the preprogrammed time. A stepper motor under control of the programmable controller steps the multiport valve head for directing water flow through the next filter. The controller also records all of the relevant parameters associated with each sampling event.
An example of such a water transfer system is the McLane Research Laboratories, Inc. McLane WTS Mark 5-18 water transfer system further described in the USER'S MANUAL WATER TRANSFER SYSTEM MCLANE WTS MARK 5-18, "Manual Version 1.43", August, 1992, by McLane Research Laboratories, Inc., 171 Clay Pond Road, Monument Beach, Mass. 02553.
A simplified diagrammatic view of an existing WTS 10 is illustrated in FIG. 1. A precision gear pump 12 with inert graphite gears is positioned on the downstream side of WTS 10 for drawing water through the WTS to avoid contamination of the sampling sites. The precision pump 12 is driven by, for example, a brushless DC servomotor whose speed is controlled by the programmable controller.
On the upstream side of the WTS 10 is the multiport valve assembly shown diagrammatically in block 14. The multiport valve 14 has a single valve head 14a with an intake port 15 through which the water or other fluid to be studied is drawn by pump 12, and multiple outlet ports 16 only one of which is open at a time by the multiport valve 14. The multiport valve assembly is coupled to a bank 18 of multiple filter holders containing respective multiple filters 20, in this example 24 in number. The respective outlet ports 16 of the multiport valve head 14a are coupled one on one to the respective filters 20 at the inlet side of the filter holders of bank 18. The outlet lines from the respective filters 20 of the bank of filter holders 18 pass through respective one way check valves 22, through a common manifold 24, and through exhaust port and manifold line 25 to the pump 12.
As subsequently described the multiport valve head 14a is typically a rotating single head valve which directs the water flow from the single intake port 15 through one of the outlet ports 16 and one of the filters 20 in the filter holder bank 18 as part of the time series sequential filter collection. A sensor such as a Hall sensor at the WTS pump drive motor, not shown, senses the pumping rate of the motor which is in turn responsive to back pressure. According to one mode of operation a programmed back pressure threshold indicates when the current filter is substantially saturated with collected suspended particles. A stepper motor coupled to the multiport valve 14 is actuated to rotate the single valve head and pass the intake water through the next filter at the programmed time. In this way the self contained WTS can be left unattended at a marine location or other water location for an extended period of time to provide the time series spectrum of sampled particles or other samples of interest.
A disadvantage of the WTS 10 of FIG. 1 is that the water flow through all of the filters 20 in the bank of filter holders 18 combines in the common manifold 24. Water flow may continue to leak through spent filters. Collected suspended particle filtrate in the spent filters may be lost by leakage into the common manifold 24. As a result the integrity of the time series spectrum of collected particles or other target samples for study may be compromised.